Archie  Clayton

Archie Clayton

1571644029

6 different ways to loop through an array in JavaScript (with examples)

Handling an array of data is unavoidable and it’s very common when it comes to building any sort of application. In this article, I’m going to show you 6 different approaches to how you can loop through an array of data in Javascript together with examples so that you can relate and later apply it in your development.

1. for Loop

The basic for loop has the following syntax:

for (initialization; condition; update statement) {
    // code block to be executed
}

The for loop statement basically uses three expressions:

  • Initialization — to initialize the loop variable with a starting value and it will only be executed once
  • Condition — defines when the loop will stop looping
  • Update Statement — is executed every time after the code block within the loop has been executed. Normally it’s being used to increment the loop variable

Note: break statement can be used to “jump out” of a for loop.

Example of using for loop:

var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

for(let i = 0; i < myArray.length; i++){
    console.log(myArray[i].name);
}

/*
Output:
    John
    Jane
    Martin
    Katie
    Louis
*/

2. for/of Loop

The for/of loop has the following syntax:

for (variable of iterator) {
    // code block to be executed
}
  • Iterator —refers to the array to be iterated
  • Variable — The value of the next iteration (if any) will be assigned to the variable. Variable has to be declared with either const, let, or var to hold the value.

Note: break statement can be used to “jump out” of a for/of loop.

Example of using for/of loop

var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

for (let profile of myArray) {
    console.log(profile.name)
}

/*
Output:
  John
  Jane
  Martin
  Katie
  Louis
*/

3. forEach()

The forEach() is an array’s method that uses a callback function to include any custom logic to the iteration. In other words, forEach() will execute the provided callback function once for each array element.

The forEach() method has the following syntax:

array.forEach(callback(currentValue [, index [, array]])[, thisArg]);
  • callback — refers to the callback function that takes up 3 arguments:
  1. currentValue — the data/value of the current element
  2. index (optional) —the array index of the current element
  3. array (optional) —the entire array object
  • thisArg (optional) — Value to be passed to the callback function which will be used as its this value.
  • Return — undefined

Note: There’s no way we can break a forEach() loop.

Example of using forEach() loop

// Example 1: Inline function
var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

myArray.forEach(function(profile, index, myArr) {
    console.log(`Index: ${index}, Name: ${profile.name}`);
});

/*
Output:
  Index: 0, Name: John
  Index: 1, Name: Jane
  Index: 2, Name: Martin
  Index: 3, Name: Katie
  Index: 4, Name: Louis
*/


// Example 2: Standalone function
var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

myArray.forEach((profile, index, myArr) => this.myfunction(profile, index, myArr));

myfunction = (profile, index, myArr) => {
    console.log(`Index: ${index}, Name: ${profile.name}`);
}

/*
Output:
  Index: 0, Name: John
  Index: 1, Name: Jane
  Index: 2, Name: Martin
  Index: 3, Name: Katie
  Index: 4, Name: Louis
*/

// Example 3: Using thisArg
this.totalAge = 0;

var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

myArray.forEach(function(profile, index, myArr) {
    this.totalAge += profile.age;
}, this);   // If "this" wasn't being included in the arguement, this.totalAge will still be 0 

console.log(`Total Age: ${this.totalAge}`);

/*
Output:
  Total Age: 67
*/

4. while Loop

The basic while loop has the following syntax:

while (condition) {
    // code block to be executed
}
  • condition — defines when the loop will stop looping

Note: break statement can be used to “jump out” of a while loop.

Example of using while loop

var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

var i = 0;
while(i < myArray.length) {
    console.log(myArray[i].name)
    i++
}

/*
Output:
  John
  Jane
  Martin
  Katie
  Louis
*/

5. do/while Loop

The do/while loop is in fact very similar to while loop. The only difference is that do/while loop will be triggered at least once regardless of the condition.

The basic do/while loop has the following syntax:

do {
    // code block to be executed
} while (condition)
  • condition — defines when the loop will stop looping

Note: break statement can be used to “jump out” of a do/while loop.

Example of using do/while loop:

var myArray = [
    {id: 1, name: 'John', age: 12},
    {id: 2, name: 'Jane', age: 14},
    {id: 3, name: 'Martin', age: 13},
    {id: 4, name: 'Katie', age: 17},
    {id: 5, name: 'Louis', age: 11}
];

var i = 0;
do {
    console.log(myArray[i].name)
    i++
} while(i < myArray.length)
  
/*
Output:
  John
  Jane
  Martin
  Katie
  Louis
*/

6. map()

At first glance, map() method is in fact very similar to forEach() method as it will also execute the provided callback function once for each array element. The only major difference is that map() method will create and return a new set of arrays based on the result of the callback function.

According to the documentation, one should use forEach() or for/of loop instead of map() method if you’re not using the newly created array it returns and/or you’re not returning a value in the callback function or else it will be considered as an anti-pattern.

The map() method has the following syntax:

var new_array = array.map(function callback(currentValue[, index[, array]]) {
    // Return element for new_array
}[, thisArg])
  • callback — refers to the callback function that takes up 3 arguments:
  1. currentValue — the data/value of the current element
  2. index (optional) — the array index of the current element
  3. array (optional) — the entire array object
  • thisArg (optional) — Value to be passed to the callback function which will be used as its this value.
  • Return — a new set of array based on the return result of the callback function

Note: There’s no way we can break a map() method.

Example of using map() method:

// Example: Inline Function
var myArray = [
    {id: 1, firstName: 'John', lastName: 'Smith', age: 12},
    {id: 2, firstName: 'Jane', lastName: 'Brown', age: 14},
    {id: 3, firstName: 'Martin', lastName: 'Johnson', age: 13},
    {id: 4, firstName: 'Katie', lastName: 'Miller', age: 17},
    {id: 5, firstName: 'Louis', lastName: 'Wilson', age: 11}
];

var newArray = myArray.map(function(profile, index, myArr) {
    var newProfile = {
        'id': index + 1,
        'fullName': profile.firstName + ' ' + profile.lastName,
        'age': profile.age
    }

    return newProfile
})

newArray.forEach(function(profile, index, myArr) {
    console.log(profile.fullName)
});

/*
Output:
  John Smith
  Jane Brown
  Martin Johnson
  Katie Miller
  Louis Wilson
*/

// Example 2: Standalone function
myfunction = (profile, index, myArr) => {
    var newProfile = {
        'id': index + 1,
        'fullName': profile.firstName + ' ' + profile.lastName,
        'age': profile.age
    }

    return newProfile
}

var myArray = [
    {id: 1, firstName: 'John', lastName: 'Smith', age: 12},
    {id: 2, firstName: 'Jane', lastName: 'Brown', age: 14},
    {id: 3, firstName: 'Martin', lastName: 'Johnson', age: 13},
    {id: 4, firstName: 'Katie', lastName: 'Miller', age: 17},
    {id: 5, firstName: 'Louis', lastName: 'Wilson', age: 11}
];

var newArray = myArray.map((profile, index, myArr) => this.myfunction(profile, index, myArr))

newArray.forEach(function(profile, index, myArr) {
    console.log(profile.fullName)
});

/*
Output:
  John Smith
  Jane Brown
  Martin Johnson
  Katie Miller
  Louis Wilson
*/

So there you have it, I have already listed down all the 6 different approaches (together with somewhat detailed explanation) on how you can loop through an array in JavaScript.

I hope that this article will be able to assist you in building your awesome applications!

#javascript

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6 different ways to loop through an array in JavaScript (with examples)

AKRAM ALEEMING

1571645388

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How to Create Arrays in Python

In this tutorial, you'll know the basics of how to create arrays in Python using the array module. Learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

This tutorialvideo on 'Arrays in Python' will help you establish a strong hold on all the fundamentals in python programming language. Below are the topics covered in this video:  
1:15 What is an array?
2:53 Is python list same as an array?
3:48  How to create arrays in python?
7:19 Accessing array elements
9:59 Basic array operations
        - 10:33  Finding the length of an array
        - 11:44  Adding Elements
        - 15:06  Removing elements
        - 18:32  Array concatenation
       - 20:59  Slicing
       - 23:26  Looping  


Python Array Tutorial – Define, Index, Methods

In this article, you'll learn how to use Python arrays. You'll see how to define them and the different methods commonly used for performing operations on them.

The artcile covers arrays that you create by importing the array module. We won't cover NumPy arrays here.

Table of Contents

  1. Introduction to Arrays
    1. The differences between Lists and Arrays
    2. When to use arrays
  2. How to use arrays
    1. Define arrays
    2. Find the length of arrays
    3. Array indexing
    4. Search through arrays
    5. Loop through arrays
    6. Slice an array
  3. Array methods for performing operations
    1. Change an existing value
    2. Add a new value
    3. Remove a value
  4. Conclusion

Let's get started!

What are Python Arrays?

Arrays are a fundamental data structure, and an important part of most programming languages. In Python, they are containers which are able to store more than one item at the same time.

Specifically, they are an ordered collection of elements with every value being of the same data type. That is the most important thing to remember about Python arrays - the fact that they can only hold a sequence of multiple items that are of the same type.

What's the Difference between Python Lists and Python Arrays?

Lists are one of the most common data structures in Python, and a core part of the language.

Lists and arrays behave similarly.

Just like arrays, lists are an ordered sequence of elements.

They are also mutable and not fixed in size, which means they can grow and shrink throughout the life of the program. Items can be added and removed, making them very flexible to work with.

However, lists and arrays are not the same thing.

Lists store items that are of various data types. This means that a list can contain integers, floating point numbers, strings, or any other Python data type, at the same time. That is not the case with arrays.

As mentioned in the section above, arrays store only items that are of the same single data type. There are arrays that contain only integers, or only floating point numbers, or only any other Python data type you want to use.

When to Use Python Arrays

Lists are built into the Python programming language, whereas arrays aren't. Arrays are not a built-in data structure, and therefore need to be imported via the array module in order to be used.

Arrays of the array module are a thin wrapper over C arrays, and are useful when you want to work with homogeneous data.

They are also more compact and take up less memory and space which makes them more size efficient compared to lists.

If you want to perform mathematical calculations, then you should use NumPy arrays by importing the NumPy package. Besides that, you should just use Python arrays when you really need to, as lists work in a similar way and are more flexible to work with.

How to Use Arrays in Python

In order to create Python arrays, you'll first have to import the array module which contains all the necassary functions.

There are three ways you can import the array module:

  • By using import array at the top of the file. This includes the module array. You would then go on to create an array using array.array().
import array

#how you would create an array
array.array()
  • Instead of having to type array.array() all the time, you could use import array as arr at the top of the file, instead of import array alone. You would then create an array by typing arr.array(). The arr acts as an alias name, with the array constructor then immediately following it.
import array as arr

#how you would create an array
arr.array()
  • Lastly, you could also use from array import *, with * importing all the functionalities available. You would then create an array by writing the array() constructor alone.
from array import *

#how you would create an array
array()

How to Define Arrays in Python

Once you've imported the array module, you can then go on to define a Python array.

The general syntax for creating an array looks like this:

variable_name = array(typecode,[elements])

Let's break it down:

  • variable_name would be the name of the array.
  • The typecode specifies what kind of elements would be stored in the array. Whether it would be an array of integers, an array of floats or an array of any other Python data type. Remember that all elements should be of the same data type.
  • Inside square brackets you mention the elements that would be stored in the array, with each element being separated by a comma. You can also create an empty array by just writing variable_name = array(typecode) alone, without any elements.

Below is a typecode table, with the different typecodes that can be used with the different data types when defining Python arrays:

TYPECODEC TYPEPYTHON TYPESIZE
'b'signed charint1
'B'unsigned charint1
'u'wchar_tUnicode character2
'h'signed shortint2
'H'unsigned shortint2
'i'signed intint2
'I'unsigned intint2
'l'signed longint4
'L'unsigned longint4
'q'signed long longint8
'Q'unsigned long longint8
'f'floatfloat4
'd'doublefloat8

Tying everything together, here is an example of how you would define an array in Python:

import array as arr 

numbers = arr.array('i',[10,20,30])


print(numbers)

#output

#array('i', [10, 20, 30])

Let's break it down:

  • First we included the array module, in this case with import array as arr .
  • Then, we created a numbers array.
  • We used arr.array() because of import array as arr .
  • Inside the array() constructor, we first included i, for signed integer. Signed integer means that the array can include positive and negative values. Unsigned integer, with H for example, would mean that no negative values are allowed.
  • Lastly, we included the values to be stored in the array in square brackets.

Keep in mind that if you tried to include values that were not of i typecode, meaning they were not integer values, you would get an error:

import array as arr 

numbers = arr.array('i',[10.0,20,30])


print(numbers)

#output

#Traceback (most recent call last):
# File "/Users/dionysialemonaki/python_articles/demo.py", line 14, in <module>
#   numbers = arr.array('i',[10.0,20,30])
#TypeError: 'float' object cannot be interpreted as an integer

In the example above, I tried to include a floating point number in the array. I got an error because this is meant to be an integer array only.

Another way to create an array is the following:

from array import *

#an array of floating point values
numbers = array('d',[10.0,20.0,30.0])

print(numbers)

#output

#array('d', [10.0, 20.0, 30.0])

The example above imported the array module via from array import * and created an array numbers of float data type. This means that it holds only floating point numbers, which is specified with the 'd' typecode.

How to Find the Length of an Array in Python

To find out the exact number of elements contained in an array, use the built-in len() method.

It will return the integer number that is equal to the total number of elements in the array you specify.

import array as arr 

numbers = arr.array('i',[10,20,30])


print(len(numbers))

#output
# 3

In the example above, the array contained three elements – 10, 20, 30 – so the length of numbers is 3.

Array Indexing and How to Access Individual Items in an Array in Python

Each item in an array has a specific address. Individual items are accessed by referencing their index number.

Indexing in Python, and in all programming languages and computing in general, starts at 0. It is important to remember that counting starts at 0 and not at 1.

To access an element, you first write the name of the array followed by square brackets. Inside the square brackets you include the item's index number.

The general syntax would look something like this:

array_name[index_value_of_item]

Here is how you would access each individual element in an array:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[0]) # gets the 1st element
print(numbers[1]) # gets the 2nd element
print(numbers[2]) # gets the 3rd element

#output

#10
#20
#30

Remember that the index value of the last element of an array is always one less than the length of the array. Where n is the length of the array, n - 1 will be the index value of the last item.

Note that you can also access each individual element using negative indexing.

With negative indexing, the last element would have an index of -1, the second to last element would have an index of -2, and so on.

Here is how you would get each item in an array using that method:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers[-1]) #gets last item
print(numbers[-2]) #gets second to last item
print(numbers[-3]) #gets first item
 
#output

#30
#20
#10

How to Search Through an Array in Python

You can find out an element's index number by using the index() method.

You pass the value of the element being searched as the argument to the method, and the element's index number is returned.

import array as arr 

numbers = arr.array('i',[10,20,30])

#search for the index of the value 10
print(numbers.index(10))

#output

#0

If there is more than one element with the same value, the index of the first instance of the value will be returned:

import array as arr 


numbers = arr.array('i',[10,20,30,10,20,30])

#search for the index of the value 10
#will return the index number of the first instance of the value 10
print(numbers.index(10))

#output

#0

How to Loop through an Array in Python

You've seen how to access each individual element in an array and print it out on its own.

You've also seen how to print the array, using the print() method. That method gives the following result:

import array as arr 

numbers = arr.array('i',[10,20,30])

print(numbers)

#output

#array('i', [10, 20, 30])

What if you want to print each value one by one?

This is where a loop comes in handy. You can loop through the array and print out each value, one-by-one, with each loop iteration.

For this you can use a simple for loop:

import array as arr 

numbers = arr.array('i',[10,20,30])

for number in numbers:
    print(number)
    
#output
#10
#20
#30

You could also use the range() function, and pass the len() method as its parameter. This would give the same result as above:

import array as arr  

values = arr.array('i',[10,20,30])

#prints each individual value in the array
for value in range(len(values)):
    print(values[value])

#output

#10
#20
#30

How to Slice an Array in Python

To access a specific range of values inside the array, use the slicing operator, which is a colon :.

When using the slicing operator and you only include one value, the counting starts from 0 by default. It gets the first item, and goes up to but not including the index number you specify.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#get the values 10 and 20 only
print(numbers[:2])  #first to second position

#output

#array('i', [10, 20])

When you pass two numbers as arguments, you specify a range of numbers. In this case, the counting starts at the position of the first number in the range, and up to but not including the second one:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])


#get the values 20 and 30 only
print(numbers[1:3]) #second to third position

#output

#rray('i', [20, 30])

Methods For Performing Operations on Arrays in Python

Arrays are mutable, which means they are changeable. You can change the value of the different items, add new ones, or remove any you don't want in your program anymore.

Let's see some of the most commonly used methods which are used for performing operations on arrays.

How to Change the Value of an Item in an Array

You can change the value of a specific element by speficying its position and assigning it a new value:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#change the first element
#change it from having a value of 10 to having a value of 40
numbers[0] = 40

print(numbers)

#output

#array('i', [40, 20, 30])

How to Add a New Value to an Array

To add one single value at the end of an array, use the append() method:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40)

print(numbers)

#output

#array('i', [10, 20, 30, 40])

Be aware that the new item you add needs to be the same data type as the rest of the items in the array.

Look what happens when I try to add a float to an array of integers:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 to the end of numbers
numbers.append(40.0)

print(numbers)

#output

#Traceback (most recent call last):
#  File "/Users/dionysialemonaki/python_articles/demo.py", line 19, in <module>
#   numbers.append(40.0)
#TypeError: 'float' object cannot be interpreted as an integer

But what if you want to add more than one value to the end an array?

Use the extend() method, which takes an iterable (such as a list of items) as an argument. Again, make sure that the new items are all the same data type.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integers 40,50,60 to the end of numbers
#The numbers need to be enclosed in square brackets

numbers.extend([40,50,60])

print(numbers)

#output

#array('i', [10, 20, 30, 40, 50, 60])

And what if you don't want to add an item to the end of an array? Use the insert() method, to add an item at a specific position.

The insert() function takes two arguments: the index number of the position the new element will be inserted, and the value of the new element.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

#add the integer 40 in the first position
#remember indexing starts at 0

numbers.insert(0,40)

print(numbers)

#output

#array('i', [40, 10, 20, 30])

How to Remove a Value from an Array

To remove an element from an array, use the remove() method and include the value as an argument to the method.

import array as arr 

#original array
numbers = arr.array('i',[10,20,30])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30])

With remove(), only the first instance of the value you pass as an argument will be removed.

See what happens when there are more than one identical values:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

numbers.remove(10)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Only the first occurence of 10 is removed.

You can also use the pop() method, and specify the position of the element to be removed:

import array as arr 

#original array
numbers = arr.array('i',[10,20,30,10,20])

#remove the first instance of 10
numbers.pop(0)

print(numbers)

#output

#array('i', [20, 30, 10, 20])

Conclusion

And there you have it - you now know the basics of how to create arrays in Python using the array module. Hopefully you found this guide helpful.

Thanks for reading and happy coding!

#python #programming 

Lowa Alice

Lowa Alice

1624406400

JavaScript Loops Tutorial

JavaScript loops made simple.

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=s9wW2PpJsmQ&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=8
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Lowa Alice

Lowa Alice

1624388400

JavaScript Arrays Tutorial. DO NOT MISS!!!

Learn JavaScript Arrays

📺 The video in this post was made by Programming with Mosh
The origin of the article: https://www.youtube.com/watch?v=oigfaZ5ApsM&list=PLTjRvDozrdlxEIuOBZkMAK5uiqp8rHUax&index=4
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Thanks for visiting and watching! Please don’t forget to leave a like, comment and share!

#arrays #javascript #javascript arrays #javascript arrays tutorial

Alverta  Crist

Alverta Crist

1590399238

How To Loop Through An Array In JavaScript

The easiest way to use for loop and forEach array method.

#javascript #javascript array #looping array #morioh

6 Ways to Add Items to an Array in JavaScript

There are various ways to add or append an item to an array. We will make use of pushunshiftspliceconcatspread and index to add items to array. Let’s discuss all the 6 different methods one by one in brief.

The push() method

This method is used to add elements to the end of an array. This method returns the new array length.

const movies = ['Avengers', 'Iron-man', 'Thor'];

const newLength = movies.push('Hulk'); 

console.log(movies); // ['Avengers', 'Iron-man', 'Thor', 'Hulk'];

console.log(newLength); //4

We can also add multiple values with push method.

const movies = ['Iron-man', 'Thor']; 

movies.push('Avengers', 'Deadpool', 'Hulk');

console.log(movies); 
// ["Iron-man", "Thor", "Avengers", "Deadpool", "Hulk"]

The unshift() method

The unshift() method is used to add elements at the beginning of an array. This method returns the new array length.

const cars = ['Audi', 'BMW', 'Jaguar']; 

const newLength = cars.unshift('Mercedes'); 
console.log(newLength ); // 4 
console.log(cars); // ['Mercedes', 'Audi', 'BMW', 'Jaguar']

We can also add multiple values with unshift() method.

const cars = ['Audi', 'Jaguar']; 

cars.unshift('Mercedes', 'Tesla'); 
console.log(cars); // ['Mercedes', 'Tesla', 'Audi', 'Jaguar']

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